Titanium base alloys



United States Patent TITANIUM BASE ALLOYS No Drawing. Application August13, 1953,

. Serial No. 374,130

6 Claims. (Cl. 75-1755) This invention relates to titanium base alloysand in particular to titanium base alloy for use at elevatedtemperatures.

Perhaps one of the most significant characteristics of the metaltitanium is its density. However, commercially pure titanium possessesrelatively low tensile strengths, viz., between 70,000 to 85,000 p. s.i. depending upon the amount of impurities contained therein. In orderto increase the mechanical properties of titanium and reduce the densityof the overall product, the element aluminum, has been alloyedtherewith. The practical limit of the binary alloy of aluminum andtitanium has been determined to be about 7.5% aluminum, since anyadditions of aluminum beyond 7.5% render the resultant binary alloycommercially unfeasible because of the difficulties encountered in thefabrication of such alloys into useful articles.

It is well-known that aluminum raises the alpha to alpha+beta and thealpha+beta to beta transus temperatures. In so doing, the alpha phase ofthe titaniumaluminum alloy exists over a broader temperature range, thuspresenting a desirable situation for the development of alloys for useat elevated temperatures. But, as was stated hereinbefore, titanium basealloys containing relatively high percentages of aluminum are difficultto fabricate. In addition, these alloys, while possessing littleductility, proved to be quite brittle after heating to a temperature inexcess of 1700 F.

In an attempt to rectify this condition, the density of the alloy wassacrificed along with elevated temperature properties of the alloy bythe addition of large percentages of beta stabilizers. Hence, thesealloys were only suitable for use below the temperature of 800 F. for,when this temperature was exceeded, the strength of the alloy decreasedat such a rapid rate that the alloy was no longer useful.

' An object of this invention is to provide a titanium base alloycontaining a substantial amount of aluminum and small but criticalamounts of beta stabilizers.

Another object of this invention is to provide titanium base'alloyscontaining aluminum and small but critical amounts of beta stabilizers,the alloys being characterized by retaining substantial ductility afterbeing heated to a forging temperature.

A further object of this invention is to provide titanium base alloyscontaining aluminum and beta stabilizers, the alloys being characterizedby excellent creep-rupture properties at elevated temperatures.

These and other objects of this invention will become apparent to thoseskilled in the art when read in conjunction with the followingspecification.

In accordance with this invention, the alloys of this invention comprisealuminum within the range from about 7.5% to about 10.0% by weight ofthe alloy, and from about 2.0% to about 3.0% of beta stabilizersselected from the group consisting of chromium, iron, molybdenum andvanadium, each of the stabilizers present in the alloy being in therange from about 0.85% to about 2,810,643 Patented Oct. 22, 1957 ice1.15% by weight of the alloy. While two of the beta stabilizers aresatisfactory in most cases, where the aluminum content is near the upperlimit of its range, three beta stabilizers are preferred. The balance ofthe alloy is composed of titanium with not more than 0.20% oxygen, notmore than 0.15% nitrogen and not more than 0.10% carbon present in theform of incidental impurities.

Reference may be had to Table I illustrating the general range, theoptimum range and two specific alloys of this invention. The twospecific alloys within the limits of this invention are identified as K1026 and K 1030.

Table I General Optimum K 1026, K 1030, Elements Range, Range, percentpercent percent percent In each of the alloys identified in Table I, thebalance is titanium with incidental impurities.

The alloys of this invention may be prepared in any suitable manner, forexample, by the well-known tungsten arc melting or consumable arcmelting processes. In

order to introduce the alloying components into the titanium base metalthat go into the make-up of the alloys of this invention, either virginmetals, aluminum master alloys or the combination of both may beemployed.

-Where tungsten arc melting is employed, the alloying com- 'of thealloy. However, the alpha phase has a close packed-hexagonacrystallographic configuration and thus exhibits little ductility. Inorder to overcome the low ductility of the close-packed-hexagonalstructure, small but critical amounts of beta stabilizers, which formthe body centered cubic crystallographic latice and which also exhibitsconsiderable ductility are employed to greatly increase the overallductility of these alloys, while at the same time not prove detrimentalto the alpha stability and creep-rupture strengths at elevatedtemperatures. In so doing, the toughness of these alloys will remainwhile at the same time provide the alloys with sufficient ductility tobe fabricated economically.

It has been found that small but critical amounts of at least two of thebeta stabilizers have a more desired effect on the alloys of thisinvention than larger percentages of any one. For example, it has beenfound that the effect of about one percent molybdenum and about onepercent chromium has a greater beneficial effect for the purpose ofthese alloys than two percent of either molybdenum or chromium. The sameapplies to the other beta stabilizers used in this invention regardlessof whether two or three beta stabilizers are used. While the reasons foraccomplishing this effect are not certain, it has been theorized thateach element has a multiplying effect on the overall alloy rather thanan additive effect.

After the molten metal has solidified to form ingots, the ingots may beprocessed by an initial step of forging. The ingots of the alloys ofthis invention are preferably heated to a temperature within the rangefrom about 3 1750 F. to about 2000 F. and thereafter forged in aconventional manner. The step of forging is employed to break-up theas-cast structure of the ingots.

In order to further hot work these tough alloys after forging, thealloys are preferably preheated to a temperature of 1400 P. where theyare held for a period of about two hours or until such time that thealloys will attain a uniform temperature of 1400" F. Of course, as iswell-known, the time required to attain a uniform temperature will varywith the bulk of the material to be heated. When the uniform temperatureis attained, the temperature is then raised to 1650 P. where it is heldfor about one-half hour or longer depending upon the bulk of the alloyand the alloys are thereafter rolled thus far encountered has been inexcess of 150,000 p. s. i. thus indicating the superiority of this alloyover and above that of the binary titanium-aluminum alloy.

However, the above mentioned properties of these alloys are roomtemperature properties. It is well-known that the mechanical propertiesof an alloy will differ at elevated temperatures from the mechanicalproperties measured at room temperature. In any true engineeringapplication involving use at elevated temperatures, the mechanicalproperties of the alloy at elevated temperatures, especiallycreep-rupture strengths, is the usual governing criteria when selectingthe proper metal to be utilized.

Reference may be had to Table III illustrating some in any conventionalmanner. 15 of the mechanical properties measured at different ele- As anexample of the heating and rolling treatments vated temperatures. Thealloys are identified as K 1026 as hereinabove described, the alloyidentified as K 1026 and K 1030, the composltlons of which have beenherein Table I was processed in the following manner: An inbefore listedin Table I.

Table II Heat Treatment T. s., T. Y. s., El R. 11., Heat Treatment T.s., T. Y. s El, R. A.,

(Air Cooled) Code p. s. i. p. s. 1. perper- Re (Air Cooled) Code p. s.i. p s. 1 perper- Rc cent cent cent cent As Rolled FEY 181,000 171,50014.0 15.5 44.4 As Forged 134,500 4.0 7.1 32.2 1 gr. 1,700: F HQ FFD 151,000 140, 000 20. 4s. a 37. 5 1 gr. (5) rggg: 12g, 500 4. 0 13. 0 32.2 1r.@1500 F. a r. 1 13 ,700 3.0 4.1 29. 24 hrs. @1.200 F i 149,000 2hrs.i,200 F DOG 147,000 143,000 5.0 0.3 32.0 2hrs. @1,450 FFE 153,500151,000 21.0 35.5 41.0 24 hrs. @1,200 F... DOH 144,300 144,300 4.7 34.021 hrs. @1,200F FFA 104,000 155,500 10.0 10.2 44.9

eleven pound ingot was forged at 1850 F. to a square size of 2.25" x2.25". The ingot, after air cooling, was

heated to a temperature of 1400 F. where it was held for a period of twohours and thereafter heated to 1650 F. The 2.25 x 2.25 ingot was held atthis temperature for one-half hour and thereafter rolled in aconventional rolling mill to a /8" round bar.

Reference may be had to Table II illustrating the room temperaturetensile properties of the alloy K 1026, here inbcfore referred to inTable I and a binary titanium base alloy containing 8% aluminumidentified as K 803, the alloys having been treated as indicated.

From the values tabulated in Table III, both the ductility and creeprupture properties of these alloys may be evaluated. It is to be notedthat in a total of 500 hours there were no failures recorded while thealloys were subjected to stresses at elevated temperature as indicated.The secondary creep rates are outstanding in exhibiting a very lowpercentage creep per hour and at the same time retaining good ductilityas measured by the bend test. It will also be noted that these alloyswere given a 1700 F. heat treatment followed by air cooling. While sucha treatment would substantially reduce what little ductility the binarytitanium-aluminum alloy possessed, it

Table III Failure El. R. A., Secondary Fh-st Alloy Code Heat TreatmentStress Temp., Time perper- Creep Rate Stage Second Stage Bend, (p. s.i.) F. (Hrs) cent cent (Pfircegnt/ Creep Creep degrees FYS hr. 1,700 F.,A. C 85,000 700 1 529 Nil Nil 0. 00023 0-30 gr 30-5000 hr., -55

.9 1. K 1026 FYI 4 hr. 1,700 F., A. o 00,000 800 1 545% Nil Nil 0. 0004oo 50-5 151".

.3 1. FYY hr. 1,700 F., A. o 85,000 700 1 50014 Nil Nil 0. 00045 000 115., 00 50 901 40-45 0. .8 K 1030 FYZ hr. 1,700 F., A. C 60,000 800 6500.1 0.67 0. 0002 011515., 15650;hr., 3045 GYF hr. 1,700 F., A. C 30, 0001, 000 1 500 Nil Nil 0.005 0-22 h? Still 0 0.8%. Running.

1 Discontinueddid not rupture.

By inspecting Table II, it is apparent that alloy K 1026 is far superiorto K 803. The only compositional difference between the two alloysresides in the fact that alloy K 1026 has about 2% of beta stabilizerspresent in its composition instead of the .5% greater aluminum contentof alloy K 803. Using the reduction of area as a criterion of ductility,it may be observed that the 2% beta stabilizers render the alloy quiteductile even after long period of heat treatment at elevatedtemperatures. It may also be observed that the 2% beta stabilizers,while increasing the ductility, also substantially increases thehardness of the alloy. The lowest tensile strength did not affect thealloys of this invention in that manner.

Particular notice should be given alloy K 1030, code GYF. This alloy wassubjected to a stress of 30,000 p. s. i. at a temperature of 1000 F.While most titanium base alloy containing large percentages of betastabilizers are not used at a temperature in excess of 800 F., thisalloy possesses excellent properties at 1000 F. as evidenced by the factthat it was still running in the test apparatus after 500 hours.

The alloy of this invention combines a number of features that makethese alloys outstanding. By making use of the low density of aluminumand alloying it with titanium along with small but critical percentagesof beta stabilizers, the overall density of the alloy is lowered. Theuse of aluminum also promotes alpha stability over a broader range oftemperatures while the beta stabilizers render the alloy suflicientlyductile to allow economical fabrication of these alloys. These alloysalso possess excellent creep-rupture strength at elevated temperatureseven after heating in a temperature range which substantially reducesthe ductility of the binary titanium-aluminum alloys.

I claim:

1. A titanium base alloy consisting of, from about 7 /2% to aboutaluminum, about 2% to about 3% of not less than two nor more than threebeta stabilizers selected from a group consisting of chromium, iron,molybdenum, and vanadium, each of the stabilizers present in the alloybeing in an amount of about 0.85% to about 1.15 and the balance beingessentially titanium with incidental impurities.

2. A titanium base alloy consisting of, from 7 /2% to 10% aluminum, from2% to 3% of not less than two nor more than three beta stabilizersselected from the group consisting of chromium, iron, molybdenum, andvanadium, each of the stabilizers present in the alloy being in theamount of about 0.85% to about 1.15%, and the balance titanium withincidental impurities.

3. A titanium base alloy consisting of, from 7 /2% to 8 /2% aluminum,from 2% to 3% of not less than two nor more than three beta stabilizersselected from a group consisting of chromium, iron, molybdenum,vanadium, each of the stabilizers present in the alloy being in anamount of about 1%, and the balance titanium with incidental impurities.

4. A titanium base alloy consisting of, about 8% aluminum, about 1%chromium, about 1% molybdenum, and the balance titanium with incidentalimpurities.

5. A titanium base alloy consisting of, about 8% aluminum, about 1% eachof iron, chromium and molybdenum, and the balance titanium withincidental impurities.

6. A titanium base alloy consisting of, about 8% aluminum, about 1%chromium, about 1% vanadium, and the balance titanium with incidentalimpurities.

References Cited in the file of this patent UNITED STATES PATENTS2,575,962 Jaffee et al. Nov. 20, 1951 2,596,485 Jafiee et al. May 13,1952 2,666,698 Dickinson et al. Jan. 19, 1954 2,700,607 Methe Jan. 25,1955 2,726,954 Jaftee et al. Dec. 13, 1955 2,739,887 Britain et al. Mar.27, 1956 2,740,711 Herres et al. Apr. 3, 1956 2,754,203 Vordahl July 10,1956 FOREIGN PATENTS 679,705 Great Britain Sept. 24, 1952

1. A TITANIUM BASE ALLOY CONSISTING OF, FROM ABOUT 71/2% TO ABOUT 10% ALUMINUM, ABOUT 2% TO ABOUT 3% OF NOT LESS THAN TWO NOR MORE THAB THREE BETA STABILIZERS SELECTED FROM A GROUP CONSISTING OF CHROMIUM, IRON, MOLBDEUM, AND VANSDIUM, EACH OF THE STABILIZERS PRESENT IN THE ALLOY, BEING IN AN AMOUNT OF ABOUT 0.85% TO ABOUT 1.15%, AND THE BALANCE BEING ESSENTIALLY TITANIUM WITH INCIDENTAL IMPURITIES. 